The invention relates generally to the field of gas turbine engine modeling. More specifically, the invention relates to methods and systems that distinguish between turbine case cooling (TCC) and high pressure turbine (HPT) performance faults.
Gas turbine performance diagnostics concerns itself with tracking changes in engine module performance measures (typically efficiency and flow parameters) as the engine deteriorates over time. The primary sources of information driving this methodology are measurements taking along the engine's gas path, such as temperatures, pressures, speeds, etc. These measurements are typically monitored during stable cruise conditions and stored for the purpose of performing a Module Performance Analysis (MPA). Because of the inherent limitation of available measurements in commercial and military aero-engines, there is a difficulty in differentiating between various faults in the turbine section of the engine. Two typical faults that fall in this category are turbine case cooling (TCC) and high pressure turbine (HPT) performance faults.
Current MPA methods use steady state cruise data to perform fault isolation. The parameters that are monitored are rotational speeds, temperatures, and pressures taken at various stages along an engine's gas path. When a shift in these measured quantities is detected, a percent Δ is computed for each gas path parameter, capturing the level and direction of the shift. The resulting vector of measurement parameter As is used to compute the MPA.
The calculation is effectively a pattern matching methodology, wherein the analysis compares the computed percent Δ vector to a series of other vectors representing known faults, and the best match is selected. This type of analysis has many methodologies and variants known in the art. Unfortunately, the signatures of HPT and TCC performance faults are nearly identical in terms of the commonly measured gas path parameters and are indistinguishable within the confines of this analysis, no matter what particular methodology is employed.
Current methods in performance tracking cannot differentiate between HPT performance faults and TCC faults. Although TCC faults are more likely to occur than HPT faults, the benign nature of a TCC fault (increased fuel consumption penalty) if improperly diagnosed may result in the engine remaining on wing with a potential for an in-flight shutdown (IFSD) or catastrophic event if the underlying cause had been an HPT problem instead. What is needed is a method and system that mitigates the risk of a TCC/HPT misdiagnosis.